Bottom line is that you're involved with someone that sees things differently than you, has a different set of priorities and values, and seems to have a different outlook on male to female relationships.



One could go into a number of reasons that there could potentially be problems in a relationship based on different variables and ruminate about how each particular potential problem should be averted by one changing, or the other but at the end of the day the question is not the problem itself it is a consensus between the partners. Without agreement on what should be done, even absent of her male friends themselves causing problems in your relationship you'll be dealing with problems in the area of being two people that do not see eye to eye in that particular area.
Can having male friends or friends of the opposite sex cause issues? yes, and they do in some cases, without question but we don't know either way whether that's an issue that will happen or not and controlling who and what type of friends your mate picks is always the wrong choice especially if they don't agree with your view.

essentially you have to accept this or move on. No other way. If you cannot find a way to accept that this is her choice, there isn't the option to bar her from male friends. If you can accept that this is the way it is, great but my impulse would be that your belief that it's a problem is not going to go away.
Find someone that shares your values and perspective on these kinds of things and you'll be much happier.